these.book

Chapter 7 ConclusionsTwo kinds of aluminum matrix composites (AMCs) based on a precipitation hardenedAl-4Cu-1Mg-0.5Ag alloy (denoted WFA) and reinforced with Al O Saffil short fibers (15%)2 3and with SiC particles (60%) have been fabricated by squeeze-casting process (SQC) for theassessment of their mechanical performance for potential automotive and electronicapplications. The composites were noted WFA/Al O /sf and WFA/SiC/p, respectively. Toward a2 3better understanding of their mechanical properties, their microstructure has been studied bytransmission electron microscopy TEM. Compared to the unreinforced alloy, the grain sizes and morphologies are stronglyaffected by the presence of the reinforcements (loss of the dendritic structure).Microsegregation mainly of Al Cu, Al Cu Fe and Q-Al Cu Mg Si is clearly visible in the as-2 7 2 5 2 8 6cast composites at the interface between the matrix and the reinforcements, and is significantlyreduced by a heat treatment at 500°C for 2 hours. In addition to its presence in the Q-phaseintermetallics, Si was detected in the matrices of all the composites. From interface reactioninvestigations by TEM, it has been deduced that Si was released from two different interfacialreactions: (1) for the WFA/Al O /sf composites, a reaction occurs between the Mg from the alloy2 3and the SiO from the Saffil fibers and from the binder of the preform when ...